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Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver

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On 5/5/2017 2:22 PM, Jassi Brar wrote:
> On Sat, May 6, 2017 at 1:23 AM, Jeffrey Hugo <jhugo@codeaurora.org> wrote:
>> On 5/5/2017 1:22 PM, Jassi Brar wrote:
>>>
>>> On Sat, May 6, 2017 at 12:07 AM, Bjorn Andersson
>>> <bjorn.andersson@linaro.org> wrote:
>>>>
>>
>> There is no way to determine if the remote processor has observed a message,
>> that does not involve pretty trivial race conditions.
>>
> Thanks for chiming in.
> How is it supposed to work if a client queues more than one request?
> How do you know when it's ok to overwrite the FIFO and send the next
> command?
>    Usually if h/w doesn't indicate, we cook up some ack packet for each
> command. Otherwise the protocol seems badly broken.
> 
>   If there is really nothing that can be done to check delivery of a
> message, I'll pick the driver as such. Best of luck :)

The protocol is designed so that we don't need an ack, or confirmation 
of delivery.  Such details are left to the higher level protocol, if 
needed.

The transmitter owns the "head" pointer in the fifo, and the receiver 
owns the "tail" pointer.  The fifo is empty if those pointers are the 
same value.  When the receiver has copied data out of the fifo, it 
advances the tail pointer.  The transmitter must ensure that the head 
pointer never meets the tail pointer through wrap around.

You can kind of check delivery based on the position of the tail 
pointer, but I can tell you from experience, you never really want to do 
that as it never tells you what you really want to know.

-- 
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

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[PATCH v4 1/5] mailbox: Make startup and shutdown ops optional Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-04 22:10 +0200
  [PATCH v4 2/5] dt-bindings: mailbox: Introduce Qualcomm APCS global binding Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-04 22:10 +0200
  [PATCH v4 4/5] soc: qcom: Add device tree binding for GLINK RPM Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-04 22:10 +0200
    Re: [PATCH v4 4/5] soc: qcom: Add device tree binding for GLINK RPM Rob Herring <robh@kernel.org> - 2017-05-08 19:10 +0200
      Re: [PATCH v4 4/5] soc: qcom: Add device tree binding for GLINK RPM Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-08 20:00 +0200
  [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-04 22:10 +0200
    Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-05 12:30 +0200
      Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-05 20:40 +0200
        Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-05 21:30 +0200
          Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jeffrey Hugo <jhugo@codeaurora.org> - 2017-05-05 22:00 +0200
            Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-05 22:30 +0200
              Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jeffrey Hugo <jhugo@codeaurora.org> - 2017-05-05 22:40 +0200
              Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-06 03:20 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-06 06:50 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-08 08:00 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-08 08:50 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-08 21:20 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-09 18:50 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-09 21:20 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-10 04:40 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-10 21:10 +0200
                Re: [PATCH v4 3/5] soc: qcom: Introduce APCS IPC driver Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-11 04:10 +0200
  [PATCH v4 5/5] rpmsg: Introduce Qualcomm RPM glink driver Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-04 22:10 +0200
  Re: [PATCH v4 1/5] mailbox: Make startup and shutdown ops optional Sudeep Holla <sudeep.holla@arm.com> - 2017-05-05 11:40 +0200
  Re: [PATCH v4 1/5] mailbox: Make startup and shutdown ops optional Jassi Brar <jassisinghbrar@gmail.com> - 2017-05-05 12:40 +0200
    Re: [PATCH v4 1/5] mailbox: Make startup and shutdown ops optional Bjorn Andersson <bjorn.andersson@linaro.org> - 2017-05-05 20:30 +0200

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